Little heat

LOWKEE

MEMBER
1998 DODGE RAM
201,456 MILES

I have a 1998 dodge ram 1500 sport. I have a problem with the heater putting out a little heat.
this is what I have done: 1) I have checked all heater doors and the are working fine. 2) I have replaced the thermostat 3 times and have checked each one before replacing them. 3) the coolent level has not gone down and is full. 4) I have checked the heater core hoses and both are hot to the touch. 5) I have used a thermometer to check the temperature of the heater core and have gotten a reading of approximately 170- 190 degrees. 6) I have even cut a small door in the heater core housing and verified that the entire core is at the temperatures stated before.
the truck does not overheat so I know the water pump is working.
what could be the problem please help.

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Wednesday, December 1st, 2010 AT 1:40 PM

31 Replies

CARADIODOC

EXPERT

I would suspect an obstruction preventing the temperature door from moving all the way to the hot setting. Measure the air temperature at the outlet. The clue is in what happens to the air temperature at different fan speeds. When the heater core is restricted, it won't be able to maintain the temperature when more air blows through it so the duct temperature will drop at higher fan speeds. If the temperature door is blocked, the percentage of hot to cold air will remain constant at any fan speed so the temperature will not change very much at different speeds.

Caradiodoc

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Saturday, April 13th, 2019 AT 5:15 PM

LOWKEE

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I am getting 90 degrees out of the vents at low fan speeds. But when on high it gets colder

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Saturday, April 13th, 2019 AT 5:15 PM

CARADIODOC

EXPERT

That suggests blockage in the heater core so not enough BTUs are making it through. What you SHOULD also find is one heater hose will be considerably cooler than the other one although in my experience that can be misleading because to me they both always feel the same.

Before you search any further, I would suggest removing the heater hoses and flushing the heater core both ways with a garden hose. If possible, take the hoses off at the engine. That will prevent spilling water onto the distributor cap if you have a V-8 or V-6 engine. It will also prevent putting strain on the heater core tubes when tugging on the hoses.

Caradiodoc

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Saturday, April 13th, 2019 AT 5:15 PM

LOWKEE

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I have flushed the heater core about 5 times. I forgot to list that. I did notice that when I took off the return line on the heater core that it seemed to trickle out of the hose when the truck was running

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Saturday, April 13th, 2019 AT 5:15 PM

CARADIODOC

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That trickle might be misleading because there isn't much pressure there pushing the coolant. The flow is achieved in a closed system because the water pump is pulling coolant just as hard as it is pushing it on the other end.

What did the flow look like with the garden hose? It should flow just as fast as the hose itself with no nozzle on the end. The heater core normally doesn't pose any restriction for a garden hose.

Caradiodoc

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Saturday, April 13th, 2019 AT 5:15 PM

LOWKEE

MEMBER

The flow with the garden hose was a constant flow both ways. I took another temp reading tonight and what I found was that when the heater was on but no fan it was about 120 degrees but as I increased fan speed the temperature dropped. When the fan was at full speed I had 90 degrees coming out of the vents.
Could the heater core be partially plugged?
All the vents are working normally.(I.E. When on defroster it goes to defroster and when on feet it goes to feet.) The temperature **** seems to be working also. When I turn to cold is seems to work fine. The only other thing I did was put the heater on ac (mine does not work) and I got a little more heat. This is begining to frustrate me.
I took a temp reading right at the heater core (behind the glove box) and I get about 170- 190 depending on how long I let the truck warm up.

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Saturday, April 13th, 2019 AT 5:15 PM

CARADIODOC

EXPERT

From everything you've written, it sure seems like the heater is partially plugged, but I've never had one yet that didn't respond to the garden hose.

Is there any way you can disconnect the actuator for the temperature door and work the door by hand? You should feel a nice soft thud as it closes each way. I know Fords have a lot of trouble with pencils falling down in the box where they block the doors. You might have leaves or a mouse nest preventing the door from sealing which would let some cold air bypass the heater core. Otherwise I'm at a loss.

Caradiodoc

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Saturday, April 13th, 2019 AT 5:15 PM

LOWKEE

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Which actuator is for the temperature? I have three vacuum actuators and a cable for the cold or warm air selector. I got 90 degrees out of it last night. I took a temp reading off my dads dodge dakota and he was putting out 120 degrees from his vents. That's a significant loss on my vehicle.
Some one said I should try and run c.L.R. Cleaners through the heater core. Do you recommend this or should I just keep trying to back flush the system?

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Saturday, April 13th, 2019 AT 5:15 PM

CARADIODOC

EXPERT

I only have a '99 service manual but it should be the same. They show three vacuum actuators for the modes, and an electric one for the temperature. You must remove the heater box to get to that one. The picture isn't clear on its location. If it is up on top to the right, you might be able to remove the glove box liner and reach in that way. It will have a two-wire electrical connector.

They make reference to the cable but they don't say what it is for. If you can see the end that attaches to the heater box, see if it slides though a stamped metal clip with three fingers. If it does, that is a self-adjusting feature. Be sure the cable isn't sliding in that clip instead of pushing on the, ... Whatever it pushes on. Once adjusted by moving its control fully both ways, that cable shouldn't slide in the clip after that.

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Saturday, April 13th, 2019 AT 5:15 PM

LOWKEE

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I do not have the electronic connector I have a cable that is connected to a door right in front of the heater core. Is this the temperature control that you talked about?

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Saturday, April 13th, 2019 AT 5:15 PM

LOWKEE

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I just checked the door and it seems to be working fine. The door has a cable on it and sits between the heater core and the ac condenser.
Does the radiator cap have anything to do with the coolant flow? I am just trying to make sure I cover all bases. The truck is running about 190 in temp. Is this okay?

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Saturday, April 13th, 2019 AT 5:15 PM

CARADIODOC

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I can't tell from the drawing, but they do talk about a cable but they don't say what it's for. They also are not clear about the location of the blend-air door actuator, only that you have to remove the heater box to get to it.

Caradiodoc

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Saturday, April 13th, 2019 AT 5:15 PM

CARADIODOC

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Sorry that the replies are out of sequence. Got tied up with a phone call.

190 is perfect. The cap shouldn't matter.

Caradiodoc

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Saturday, April 13th, 2019 AT 5:15 PM

LOWKEE

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I can see the blend door connecting arm and I think it is connected with a cable. You would have to take the dash apart in order to get to it. But you can get a hand on the lever and I checked it and it is working and making a sound when moved.
I have a stupid question and that is could my ac be stuck on and causing cold air to flow through the heater although I am asking it to pump heat? Or am I grasping at straws here.

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Saturday, April 13th, 2019 AT 5:15 PM

CARADIODOC

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The AC will run in defrost mode to remove humidity from the air before it blows it onto the cold windshield. Other than that, you should not see the compressor cycling on in heat or vent modes.

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Saturday, April 13th, 2019 AT 5:15 PM

LOWKEE

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Okay. I checked the ac to see if the compressor was cycling on in the heat modes and it was not I checked in the defrost mode and it cycled quickly. The ac doesn't work anymore.

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Saturday, April 13th, 2019 AT 5:15 PM

CARADIODOC

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There must be a little charge in the system if it cycled on at all. It wouldn't matter anyway. The AC evaporator in the dash is limited to 40 degrees so condensation won't freeze into a block of ice and block air flow. In heat mode, it is taking potentially minus 30 degree outside air and warming it up to a comfortable level, so in defrost mode, it only would have to overcome plus 40 degree air from the evaporator. That's no different than taking 40 degree outside air and raising it up.

Caradiodoc

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Saturday, April 13th, 2019 AT 5:15 PM

LOWKEE

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I am at a loss in what to do next. Any ideas? I think I might have to bite the bullet and disassemble the dash.
I wish there was a way to definitely tell if the heater core was clogged or not.

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Saturday, April 13th, 2019 AT 5:15 PM

CARADIODOC

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The only thing I can think of to try would be to pinch off the upper radiator hose for a minute or two to bring the coolant temperature up closer to 200 degrees and see how the air feels. Ten degrees can be quite a difference, especially when you're freezing your butt off planting insulation! I hate winter!

Caradiodoc

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Saturday, April 13th, 2019 AT 5:15 PM

LOWKEE